| Message ID | 20241023121145.1321921-6-jfalempe@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | drm/log: Introduce a new boot logger to draw the kmsg on the screen | expand |
On Wed 2024-10-23 14:00:13, Jocelyn Falempe wrote: > The console is already suspended in printk.c. Does this mean that drm_log_client_suspend() is called after suspend_console(), please? By other words, does it mean that "dlog->suspended == true" is set only when CON_SUSPENDED is already set in the related con->flags? > Just make sure we don't write to the framebuffer while the graphic > driver is suspended. > It may lose a few messages between graphic suspend and console > suspend. The messages should not get lost when the console is properly suspended by suspend_console(), set CON_SUSPENDED. Or maybe, I do not understand it correctly. Maybe you want to say that it should work correctly even without this patch. And this patch creates just a safeguard to make sure that nothing wrong happens even when suspend_console() was not called from some reasons. Note: I tried to check the order by reading the code. But drm_log_client_suspend() was called via too many layers. And I was not able to find where exactly it was called, for example, from hibernate() in kernel/power/hibernate.c > --- a/drivers/gpu/drm/drm_log.c > +++ b/drivers/gpu/drm/drm_log.c > @@ -310,10 +311,32 @@ static int drm_log_client_hotplug(struct drm_client_dev *client) > return 0; > } > > +static int drm_log_client_suspend(struct drm_client_dev *client, bool _console_lock) > +{ > + struct drm_log *dlog = client_to_drm_log(client); > + > + mutex_lock(&dlog->lock); > + dlog->suspended = true; > + mutex_unlock(&dlog->lock); It might also be possible to explicitly set the CON_SUSPENDED flag here to be always on the safe side. We could create variant of suspend_console() just for one console. Something like: void suspend_one_console(struct console *con) { struct console *con; if (!console_suspend_enabled) return; pr_info("Suspending console(%s) (use no_console_suspend to debug)\n"); pr_flush(1000, true); console_list_lock(); if (con && console_is_registered_locked(con)) console_srcu_write_flags(con, con->flags | CON_SUSPENDED); console_list_unlock(); /* * Ensure that all SRCU list walks have completed. All printing * contexts must be able to see that they are suspended so that it * is guaranteed that all printing has stopped when this function * completes. */ synchronize_srcu(&console_srcu); } and call here: suspend_one_console(dlog->con); But this is not needed when the console is already supposed to be disabled here. If this is the case then it might be better to just check and warn when it does not happen. Something like: void assert_console_suspended(struct console *con) { int cookie; cookie = console_srcu_read_lock(); /* Do not care about unregistered console */ if (!con || hlist_unhashed_lockless(&con->node)) goto out; if (WARN_ON_ONCE(!(console_srcu_read_flags(con) & CON_SUSPENDED))) pr_flush(1000, true); out: console_srcu_read_unlock(cookie); } > + return 0; > +} Best Regards, Petr PS: I have vacation the following week and might not be able to follow the discussion before I am back.
On 24/10/2024 16:34, Petr Mladek wrote: > On Wed 2024-10-23 14:00:13, Jocelyn Falempe wrote: >> The console is already suspended in printk.c. > > Does this mean that drm_log_client_suspend() is called > after suspend_console(), please? To be honest, I wasn't able to tell which one is called first, and if the order is enforced (I didn't check if drivers can be suspended in parallel, or if it's all sequential).. I then checked if it's possible to suspend the console, but didn't found an easy API to do so, so I went with this lazy patch, just ensuring we're not writing to a suspended graphic driver. > > By other words, does it mean that "dlog->suspended == true" is set > only when CON_SUSPENDED is already set in the related con->flags? > 8 >> Just make sure we don't write to the framebuffer while the graphic >> driver is suspended. >> It may lose a few messages between graphic suspend and console >> suspend. > > The messages should not get lost when the console is properly > suspended by suspend_console(), set CON_SUSPENDED. > > Or maybe, I do not understand it correctly. Maybe you want to say > that it should work correctly even without this patch. And this > patch creates just a safeguard to make sure that nothing wrong > happens even when suspend_console() was not called from some > reasons. I mean that with this patch if the console is suspended after the graphic driver, then the message between the suspend of the graphic driver and the suspend of the console won't be drawn. I don't see that as a big problem, if you debug suspend/resume with drm_log, and the screen goes blank, you won't see much anyway. And using dmesg when the system is resumed, would have all the messages. Without this patch, it may crash if the framebuffer is no more accessible, and drm_log tries to draw a new line on it. > > > Note: I tried to check the order by reading the code. But > drm_log_client_suspend() was called via too many layers. > And I was not able to find where exactly it was called, > for example, from hibernate() in kernel/power/hibernate.c > > >> --- a/drivers/gpu/drm/drm_log.c >> +++ b/drivers/gpu/drm/drm_log.c >> @@ -310,10 +311,32 @@ static int drm_log_client_hotplug(struct drm_client_dev *client) >> return 0; >> } >> >> +static int drm_log_client_suspend(struct drm_client_dev *client, bool _console_lock) >> +{ >> + struct drm_log *dlog = client_to_drm_log(client); >> + >> + mutex_lock(&dlog->lock); >> + dlog->suspended = true; >> + mutex_unlock(&dlog->lock); > > It might also be possible to explicitly set the CON_SUSPENDED flag > here to be always on the safe side. We could create variant of > suspend_console() just for one console. Something like: > > void suspend_one_console(struct console *con) > { > struct console *con; > > if (!console_suspend_enabled) > return; > > pr_info("Suspending console(%s) (use no_console_suspend to debug)\n"); > pr_flush(1000, true); > > console_list_lock(); > if (con && console_is_registered_locked(con)) > console_srcu_write_flags(con, con->flags | CON_SUSPENDED); > console_list_unlock(); > > /* > * Ensure that all SRCU list walks have completed. All printing > * contexts must be able to see that they are suspended so that it > * is guaranteed that all printing has stopped when this function > * completes. > */ > synchronize_srcu(&console_srcu); > } > > and call here: > > suspend_one_console(dlog->con); > > > But this is not needed when the console is already supposed to be > disabled here. If this is the case then it might be better > to just check and warn when it does not happen. Something like: > > void assert_console_suspended(struct console *con) > { > int cookie; > > cookie = console_srcu_read_lock(); > > /* Do not care about unregistered console */ > if (!con || hlist_unhashed_lockless(&con->node)) > goto out; > > if (WARN_ON_ONCE(!(console_srcu_read_flags(con) & CON_SUSPENDED))) > pr_flush(1000, true); > out: > console_srcu_read_unlock(cookie); > } > >> + return 0; >> +} > > Thanks for this two suggestions, this is really what I was looking for. I will run some tests on real hardware, to see which one is suspended first. Best regards,
On 25/10/2024 01:11, Jocelyn Falempe wrote: > On 24/10/2024 16:34, Petr Mladek wrote: >> On Wed 2024-10-23 14:00:13, Jocelyn Falempe wrote: >>> The console is already suspended in printk.c. >> >> Does this mean that drm_log_client_suspend() is called >> after suspend_console(), please? > > To be honest, I wasn't able to tell which one is called first, and if > the order is enforced (I didn't check if drivers can be suspended in > parallel, or if it's all sequential).. > > I then checked if it's possible to suspend the console, but didn't found > an easy API to do so, so I went with this lazy patch, just ensuring > we're not writing to a suspended graphic driver. I've run some tests on my hardware, and the console is suspended before the graphic driver: [ 56.409604] printk: Suspending console(s) (use no_console_suspend to debug) [ 56.411430] serial 00:05: disabled [ 56.421877] sd 0:0:0:0: [sda] Synchronizing SCSI cache [ 56.421954] sd 4:0:0:0: [sdb] Synchronizing SCSI cache [ 56.422545] ata1.00: Entering standby power mode [ 56.422793] DRM log suspend But because there is the "no_console_suspend" parameter, and we should make sure to not draw when the graphic driver is suspended, I think this patch is needed, and good enough. I will just rephrase the commit message, to make it clear, that some message won't be drawn, only if "no_console_suspend" is set. Best regards,
diff --git a/drivers/gpu/drm/drm_log.c b/drivers/gpu/drm/drm_log.c index 635dff7b37ce5..07d1513001468 100644 --- a/drivers/gpu/drm/drm_log.c +++ b/drivers/gpu/drm/drm_log.c @@ -50,6 +50,7 @@ struct drm_log { struct drm_client_dev client; struct console con; bool probed; + bool suspended; u32 n_scanout; struct drm_log_scanout *scanout; }; @@ -310,10 +311,32 @@ static int drm_log_client_hotplug(struct drm_client_dev *client) return 0; } +static int drm_log_client_suspend(struct drm_client_dev *client, bool _console_lock) +{ + struct drm_log *dlog = client_to_drm_log(client); + + mutex_lock(&dlog->lock); + dlog->suspended = true; + mutex_unlock(&dlog->lock); + return 0; +} + +static int drm_log_client_resume(struct drm_client_dev *client, bool _console_lock) +{ + struct drm_log *dlog = client_to_drm_log(client); + + mutex_lock(&dlog->lock); + dlog->suspended = false; + mutex_unlock(&dlog->lock); + return 0; +} + static const struct drm_client_funcs drm_log_client_funcs = { .owner = THIS_MODULE, .unregister = drm_log_client_unregister, .hotplug = drm_log_client_hotplug, + .suspend = drm_log_client_suspend, + .resume = drm_log_client_resume, }; static void drm_log_write_thread(struct console *con, struct nbcon_write_context *wctxt) @@ -321,6 +344,9 @@ static void drm_log_write_thread(struct console *con, struct nbcon_write_context struct drm_log *dlog = console_to_drm_log(con); int i; + if (dlog->suspended) + return; + if (!dlog->probed) drm_log_init_client(dlog);
The console is already suspended in printk.c. Just make sure we don't write to the framebuffer while the graphic driver is suspended. It may lose a few messages between graphic suspend and console suspend. Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com> --- drivers/gpu/drm/drm_log.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+)